In vitro evaluation of the effect of temporary removal of HIV drug pressure

We tried to establish whether MT-4 cells that were infected with HIV-1(HTLV -IIIB) at a high multiplicity of infection (m.o.i. = 1), and subsequently t reated with high concentrations of anti-HIV drugs for several days, would b e able to resume virus projection after the antivirals are washed away. The HIV inhibitors studied were the nucleoside reverse transcriptase inhibitor s (NRTIs) zidovudine and lamivudine, the non-nucleoside reverse transcripta se inhibitors (NNRTIs) nevirapine, delavirdine and loviride, the acyclic nu cleoside phosphonate RT inhibitor (R)-9-(2-phosphonylmethoxypropyl)adenine (tenofovir) and the protease inhibitors (PIs) saquinavir, indinavir and rit onavir. The compounds, at 50 and 500 times their 50% inhibitory concentrati on (IC50, determined at a m.o.i. = 0.01), were added immediately after viru s adsorption and removed after an incubation period of 0 (wash control), 24 , 48 or 72 h. Virus breakthrough was monitored by microscopical examination of cytopathicity, viral infectivity (yield) and p24 levels in the supernat ant. The presence of HIV-1(HTLV-IIIB) proviral DNA was determined after a 7 2-h incubation period. None of the antiviral drugs studied was able to prev ent resumption of viral growth after removal of the compound. Tenofovir, la mivudine and the NNRTIs nevirapine, delavirdine and loviride, at 500 times their respective IC50, were able to delay viral breakthrough for approximat ely 2-3 days. The NRTI zidovudine and the PIs saquinavir, indinavir and rit onavir, under the same conditions, were not able to delay viral breakthroug h at all. Virus recovered upon treatment proved as sensitive to the anti-HI V drugs as wild-type virus. Our results suggest that viral replication at t he cellular level was not completely inhibited by drug monotherapy. Consequ ently, virus rebounded when drug therapy stopped. In conclusion, our findin gs suggest that drug holidays would result in viral breakthrough, even afte r virus replication has been previously suppressed by adequate drug levels. (C) 2000 Elsevier Science B.V. All rights reserved.